Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~4~85
~.~SS-TRANSFER APPARATUS
The invention relate~ to chemical and petroleum en-
gineering and has specific reference to mas~-tran~fer appa-
ratu~.
The invention can be of utility in Yarious installa-
tions for heat and mas~ tran~fer ~etween a liquid ~nd a ga9
which find applicatio~ in the chemicalj gas, petroleum ri-
fining, metallurgical and ~ood indu~trie~ as well as in oth-
er field~. rrhe apparatu~ di~clo~ed can cope with the proces~-
e~ o~ absorption, fractination, desorption and ~as scrubb-
ing.
The invention holds out ~pecial promise as an item of
the equipment of gas-procesaing plant~ and separate in~talla-
tions u~ed in the oil and gas industry for treating natural
ga~ aLd condensate preparatory to conveying over long dis-
tance B -
Cryogenic ~ir-separation plant~ is a prO~peCtiVe field
of application of the invention.
A sharp increase in the capacity and ef~ectivenes~ of
mass-tran~er columns i~ a problem nowaday~. The point i8
that the bubble trays of the traditional de~ign u~ed in
these columns do not permit the flow rate of gas or vapour
through the net cross-~ectional area of a column to be in-
creased oYer a given minimum, which i8 1.2-1.5 mJs for an
air-water system under the atmospheric conditions. The prob-
lem i~ coped with by increasing the diameter of ma~s-trans-
fer apparatus which can be a~ large as 3 to 12 m in high-
1264X85
-capacity in~tallations.
Thi~ approach iB, however, unacceptable for drilling
ships and offshore rigs where ~pace is at premium.
Xnown in the art i~ a ma~-tran~fer apparatus for ga~-
to-liquid contact in the ca3e whereof there are contained
one perforated tray, or several ~uch tray~, Qnd a sprayer
(cf. Pozin ~.E. "Pennye ~azoochi~titeli, teploobmenniki 1
absorbery", Ieningrad, 1959, p. 51).
A liquid fed from the ~prayer forms a layer of mobile
froth on the tray to ab~orb certain gases or dust from the
bulk gas flow.
The capacity of the known apparatu~ is low, for the flow
rate of the gas through the net cross-aectional area theIe-
of is slow, commonly not over 2 or 2.3 m/8, and the layer
of froth on the tray i8 thin (around 100 mm).
Any attempt to boost the capacity gives ri~e to tur-
bulence which leaves some portions of the tray uncovered
with the froth, permittin~ some of the gas to pass through
the tray unprocessed. This reduce~ the effectivene~a of the
apparQtus.
Also known is a mass-tran~fer apparatue which, in addi-
tion to heat and mass tran~fer, can cope also with the wet
8crubbing of gase~ (cf. USSR Inventor'~ Certi~icate
No. 434,969, Int. Cl. B01 d 47/04). The ca~e of the known
apparatus contains perfor~ted tray~ each whereo~ is ~itted
with a contiguous froth retainer in the form of a grid made
up of upright barA. The height of ever~ bar i8 0.2 to 0.6
time the thickne~ of the froth layer, and the net cross-
~X64;~85
-- 3 --
-eectional area of a grid is at lea~t 0.8 time the net eros3-
_eectional area of the apparatus. 2erforation~ are provided
in some of the bsrs of the froth retainer, next to the sur-
face of the tray.
The main purpose the froth retainer is to set up on
the tray a thick and ho~ogenous layer of froth vJith fine
cellular ~tructure and to pro~ide for a continuous flow of
the phases at their interface without spparent fluctuation~.
In other ~Jord~, the ~roth retainer eliminate turbulence and,
con~equently, increase the capacity of the apparatus.
Ho~ever, the effectiveness of the process of heat and
mas~ transfer taking place in the known apparatus at the gas
flow rates over 2.6 to 3.0 m/~ iB low (for the air-water
syRtem under the atmo~pheric conditions). Intermittent eddi-
e~ brou~ht about at the top of the froth layer expel eome
of the liquid from grid cells along the axes thereof, render-
ing this portion ineffective as a medium for an active mass
transfer or dust recovery. An accompanying splashing im-
pair~ the capacity of the apparatu~ and the effectivenes~ of
ma~ transfer proce~ses.
The perforations in the lower portion~ of some bars
of the froth retainer cannot provide for a u~iform di~tri-
bution of the liquid flow over the entire surface of the
trsy.
The main object of the inYention i~ to provide a ma~e-
transfer apparatu~ a froth retainer whereof i8 deBigned
ao as to increase both the capacity and the ef~ecti~eneee
of the apparatus, uniformly distribute the liquid in the
form of a froth with fine cellular structure over the en-
64~ 85
-- 4 --
tire surface of ~ tray and prevent splQ3hing of the liquidalong the a~es of grid cells should the g~ flow rate be
speeded up.
~he essence of the invention consists in that in a mas~-
-transfer spparatu~ in the ca~e whereof there are contained
at least one horizontal perforated tray and a froth retain-
er in the forn of a grid made up of upright bars which are
fitted directly to the tray and form intercom~ected cells,
according to the invention the lower portions of the bar~
of the froth retainer are made solid and the cell~ of the
grid communicate with one another by way of perforations
in the upper portions of the bars of the froth retainer.
The perforations flowing wherethrough from one cell
to another i~ the froth exercise a self-instituted flow
control owing whereto the liquid ie uniformly distributed
over the relatively great area of the tray. The ~olid por-
tions of the foam retainer bar~ ~erve the same purpo~e
as well, preventing undesired accumulations of the liquid
in depre~sions or at obliquities of the tray.
It is expedient that the solid portions of the bar~
of the froth retainer are of a height which is 0.1 to 0.5
time the overall height of these bars.
~ his plan is conducive to a u~iform distribution of
the froth layer over the entire surface of the tray.
It i~ also expedient that the ratio of the total net
area of the perforations in the froth retainer and that of
the perforations in the trag i~ 1.2-3Ø This ratio provid-
es for a dependable self-instituted control of the froth
12~4~85
-- 5 --
layer when the liquid overflows from one call to ~nother.
It is further expedient that the height of the froth
retsiner i~ 0.6-1.0 time the distance between two trays,
provided the apparatus has more than one tray.
The froth retainer standing as high as that provides
for an effective operation of the mas~-transfer apparatu~
over a wide range o~ gas floYJ rate~.
In small-diameter apparatus, the froth retainer can
extend over the entire distance ~eparatin~ tvJo adjacent
trays. In lar~e-diameter apparatus, it is practical that
the height of the froth retainer i6 some~Jhat smaller than
the di~tance between the tray~. An unobstructed ~pace ~o
formed permits a redi~tribution of the ~as (vapour) flow
to take place before the gas reaches the above-lying trsy.
It is preferred that at least two diagonal baffle
plates located crosswise one above the other are provided
in every cell of the froth retainer, the height of every
baffle plate equalling at least one half of the length of
a cell side.
The liquid striking against a baffle plate spread~
thereover and i~ deflected towards cell walls so that no
azialwise splashing is brought about. The proce~s is re-
peated at a ~uperimposed cruciform baffle plate which en-
hances the spla~h-depressing effect. A steady froth stabi-
lity is the outcome even in large cell~.
It is also preferred that at least one cruci~orm baf-
fle plate is provided in every cell, with the height of
this baffle plate equalling at lea~t one half of the length
2 64~ ~5
-- 6 --
of a cell ~ide.
The cruciform baffle plate ~uppresse~ the spla~hing
better than a diagonal one does, providing for an increaee
in the capacity of the ma~s-transfer apparatu~. This is
achievable by increasing either the size of cells or the
gas (vapour) flow rate, without changing the size of cell~
in this latter case.
It i~ further preferred that the ba~fle platea in the
cells are perforated.
The perforated baffle plates have a better showing
than solid onee in suppressing the splashing and l~eeping
up the froth i~ the cells. Their performance permit~ the
flow rate of gas or vapour to be increased in the appara-
tus.
A preferred embodiment of the invention will now be
described by way of an example with reference to the accom-
panying drawings in which
Fig. 1 ie a sectional elevation of the apparatu~ ac-
cording to the invention;
Fig. 2 is an axonometric view of a froth retainer;
Fi~. 3 iB a sect~onal elevation of a cell of a froth
retainer showing a cruciform baffle plate at the top and
two diagonal ba~fle plates below it;
Fig. 4 is a seotion on line IV-IV of Fig. 3;
Pig. 5 is an axonometric view of a diagonally-srrang-
ed cruciform baffle plate in a cell;
Fig. 6 is an axonometric view of two diagonal baffle
plates located a distance apart.
12~fiS
-- 7 --
Referring to Fig. 1, a caee 1 of the mass-transfer ap-
paratu~ of a rectangular or circular eection is fitted with
ga~ inlet and outlet pipe~ 2, 3 and a union 4 through which
spent liquid leave~ the apparatus. A sprayer 5 i~ located
in the case 1 abo~e a horizontal perforated tray 6 formed
and kept up whereon is a l~yer of froth. The perforated tray
6 is made up either of perforated sheets or separate tu~e~
(rods) whic~l form a regular grid. A froth retainer 7 made
up of up-right bars 8 con~tituing a grid with ce 119 9 is
fitted directly to the tray 6.
A length C of a side of the ~quare cell 9 is 0.08-
-0.25 time a height B of the cell side.
IhR maa~-transfer apparatus of Fig. 1 is fitted with
two trays but, according to the invention, there can be on-
ly o~e tray or more than t~o trays. In an apparatu~ with two
or more trays, the height ~ of the froth ret~iner 7 is 0.6-
-1.0 time a di~tance H between two adjacent tray~ 6.
Referring to Fig. 2 which i8 an a~onometric view of a
froth retainer 7, the cell~ 9 thereof communicate with one
another via perforations 10 provided at the top of the bars
8, whereas the lower portions of the bars 8 (Fig. 3) are
made solid. A height F of the solid portion of every bar
8 i~ 0.1-0.5 time the height B of the bar 8.
~ he way the perforations 10 are arra~ged in the bars
8 of the froth retainer 7 is shovln in detail in Fig. 3
which is a sectional elevatlon o~ the cell 9. ~he number
and diameter of the perforations 10 are selected 80 that
the ratio of the total net area of the perforations 10 i~
12~4X~s
- ~ -
the froth retainer 7 and that of the perforations in the
tray is 1.2-3Ø
h cruciform baffle plate ll formed by bars 12, 13 which
run parallel with the bars 8 of the froth retainer 7 is fit-
ted at the top of the cell 9.
Diagonal baffle plates 14,15 are fltted below the
cruciform baffle plate ll and a di~tance apart ~rom each
other.
Fig. 4 illustratea a version of the cruciform baffle
plate 11 the bar~ 12, 13 whereof are secured parallel with
the bar~ 8 (Fig. 1) of the froth retainer 7.
Fig. 5 illustrate~ diagonal ba~fle plates 14, 15 which
are located in the cell 9 (shown in light lines) of the
froth retainer 7 out of contact with one another. However,
diagonal bsffle plate~ located in contact with one another
pro~ide a possible alternative.
Fig. 6 illustrates a veraion of a cruciform baffle
plate 16 with diagonal bars 17~ 18 located inside a cell 9
(~ig. l~ of the froth retainer 7 shown in light lines.
Cruciform baffle plates located parallel with the bars
of the froth retainer (Fig. 4~ and those coincidi~g with
the diagonals of the cell (Fig. 5) are of e~ual value as
far as their per~ormance is conc~rned. The optio~ depends
on the process of manufacturing the froth retainers.
The baffle plates shown in Fig~.-3 through 6 are made
of ~olid bars but perforated baffle plates ca~ be used as
well. In this latter case they are not only lighter but
more effective as means of chec~ing the ~plashing of liquid
~2~XBS
in the cells, providin~ for good performance of the mass-
tran~fer apparatus at maximum gas flo~ rates.
In operation, the ga~ or vspour admitted through the
pipe 2 pasæes through the perforated tray 6, contacting
there the liquid fed through the sprayer 5.
A layer of froth formed on the tray ~ due to the agita-
tion of the liquid by the ga~ i8 of fine cellular ~tructure
owing whereto the processe~ of heat and mass transfer, and
also of ga~ scrubbing, go on at a high rate. ~he 6crubbed
gas leaves the apparatu~ through the pipe 3 and the liquid,
through the union 4.
~ luctuation~ in the depth of the liquid on the tray 6
due to non-uniform feeding thereof are off~et due to the
circulation of the liquid between the cell~ of the froth re-
tainer 7.
If the trays used are of a large diameter it iB prac-
tical to provide a free space above the froth retainer to
uniformly supply the gas to the above-lying trag. In small-
diemeter mass-tran~fer apparatus, the froth retainer can ex-
tend through the total distance between two adjacent trays.
The diagonal or cruciform baffle plates provided inside
the cells of the froth retainer control the turbulence at
the centre~ of the cell~, whi~h gives rise to splashing,snd
promote the ~tability of the layer of froth. Perforated baf-
fle plates are particularly effective in thi~ respect, re-
t~ining and redi~tributing the froth in a better way than
their solid counterparts. The apparatus with perfor~ted d~-
agonal or cruciform baffle plate~ in the cells of the froth
- .
12642~35
- 10 -
retainer operate at a maximum gas (vapour) flow rate which
cannot be achieved in mass-transfer apparatus featuring
froth retainers of any other de~ign.
The disclo~ed mas~-transfer apparatus provideR solution
to the problem of increasing 1.5 to 2 times the capacity of
absorption and desorption pla~lts, fractination units and
gas scrubbin~ equipment.
Apart from that, the disclosed apparatus improves pro-
duct purity owing to a high effectivene~s of the mechani~m
of heat and ma~s tran~fer therein.
~ he pre~ent invention is conducive to increasing the
capacity of the mass-transfer colum~, ~hich i~ the key item
of a mass-transfer inEtallation, and pave~ the way to deve-
loping compact plants ~ith a large capacity per unit volume.
The invention can be used to advantage in the chemical, pe-
trochemical, food, oil and gas industires to cope with ma~s-
-transfer proces~es.
A preferred field of its application comprises de-etha-
nizers and ~tabilizers for processing condensate, high-pres-
sure absorbers for treating natural ga~, fractination cOlUmn8
used in the manufacture of synthetic rubber, cryogenic air-
_separation plants and gas scrubbers.
